Internet DRAFT - draft-mankamana-pim-graceful-dr-shutdown
draft-mankamana-pim-graceful-dr-shutdown
Network Working Group Mankamana. Mishra
Internet-Draft Stig. Venaas
Intended status: Standards Track Cisco Systems
Expires: January 3, 2019 Mahesh. Sivakumar
juniper networks
Zheng(Sandy). Zhang
ZTE Corporation
Mikael. Abrahamsson
July 2, 2018
PIM Designated Router graceful shutdown
draft-mankamana-pim-graceful-dr-shutdown-00
Abstract
On a multi-access network, one of the PIM routers is elected as a
Designated Router (DR). On the last hop LAN, the PIM DR is
responsible for tracking local multicast listeners and forwarding
traffic to these listeners if the group is operating in PIM-SM. In
case of a network maintenance, where we want to bring down the
current DR, there is currently no way to gracefully handover the PIM
DR role to a new DR on the shared LAN. In this document, we propose
a modification to the PIM-SM protocol that allows PIM DR to
gracefully shutdown or go down for maintenance. We also provide a
procedure for PIM DR to gracefully handover its role to a new PIM DR
in the network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 3, 2019.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Specification . . . . . . . . . . . . . . . . . . . 4
3.1. Proposed Mechanism . . . . . . . . . . . . . . . . . . . 4
3.2. Impact on the network . . . . . . . . . . . . . . . . . . 4
3.2.1. Every PIM router supports the new specification on
the shared LAN . . . . . . . . . . . . . . . . . . . 4
3.2.2. Hybrid shared LAN, some of PIM router does not
support specification . . . . . . . . . . . . . . . . 5
4. PIM Hello option . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
On a multi-access LAN such as an Ethernet, one of the PIM routers is
elected as a DR. The PIM DR represents the LAN segment/broadcast
domain in the PIM topology tree and has two roles to play in the PIM-
SM protocol. For sources connected to the segment, the PIM DR is
responsible for registering one or more active sources with the
Rendezvous Point (RP) if the group is operating in PIM-SM. In
addition, on the last hop LAN, the PIM DR is responsible for tracking
local multicast listeners and forwarding data traffic to these
listeners if the group is operating in PIM-SM.
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Consider the following last hop LAN in Figure 1:
( core networks )
| | |
| | |
R1 R2 R3
| | |
--(last hop LAN)--
|
|
(many receivers)
Figure 1: Last Hop LAN
Assume R1 is elected as the Designated Router. According to
[RFC4601], R1 will be responsible for forwarding traffic to that LAN
on behalf of any local members. In addition to keeping track of IGMP
and MLD membership reports, R1 is also responsible for initiating the
creation of source and/or shared trees towards the sources or the
RPs.
If R1 needs to go on planned maintenance, the current approach is to
lower the DR priority which would make sure that another PIM router
on the LAN gets elected as the new DR and starts forwarding multicast
traffic.
With this approach, R1 gives away DR role as soon as new priority is
configured and a new PIM DR (lets assume R3) starts building a
multicast tree and starts forwarding multicast traffic on the LAN.
However, this could cause traffic disruption for the duration it
takes for R3 to build the upstream multicast tree.
This draft defines a mechanism in the PIM protocol to handover DR
role gracefully and as a result minimize traffic disruption.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] .
With respect to PIM, this document follows the terminology that has
been defined in [RFC4601] and [RFC7761] . Many places this draft
would refer to PIM RFC [RFC4601] but it MUST be considered [RFC7761]
as well.
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3. Protocol Specification
In this draft, we define a new hello option to enable the graceful
handover of a DR during planned maintenance.In Section 3.1, we
describe the proposed mechanism. In Section 3.2, we evaluate the
impact of the mechanism on the network under different conditions.
Section 4 describes the proposed hello option.
3.1. Proposed Mechanism
1. In Figure-1, assume that R1 is current PIM DR that needs to go on
planned maintenance. R1 MUST sends out a PIM Hello with option
described in Section 4. The DR Priority MUST be set to 0. R1
MUST also set its assert metric to (PIM_ASSERT_INFINITY - 1)
2. The PIM assert metric modification would make sure that R1 does
not become an assert winner
3. Sending DR priority as 0 would make sure to have default
transition in case new DR does not support the new specification
4. The current PIM DR (R1 here) MUST not stop forwarding traffic to
intended receivers unless it starts getting duplicate flows from
newly elected PIM DR.
5. A failsafe timer SHOULD be used to stop forwarding multicast
traffic towards receiver. It SHOULD be set to at least two PIM
Hello intervals. But it SHOULD also be a configurable value.
3.2. Impact on the network
This section covers impact of PIM hello with Section 4 option
3.2.1. Every PIM router supports the new specification on the shared
LAN
1. In Figure-1, if each of the PIM routers on shared LAN supported
this specification, new DR election would be done as per
[RFC4601]
2. The newly elected DR MUST start building the multicast tree
towards the source/RP. It MUST start fail safe timer (default
value 2 PIMHello interval) and MUST not generate a data driven
assert. Once the timer expires, it can move back to the default
assert mechanism. The reason to avoid an assert is to allow the
old PIM DR on LAN to forward multicast traffic until such time
the new DR is completely ready to forward multicast traffic.
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3. It MUST forward multicast flow to receivers as soon as it gets
the multicast flow from the source/RP
3.2.2. Hybrid shared LAN, some of PIM router does not support
specification
There are two cases to consider,
1. If the new DR supports this specification, it would follow
Section 3.1
2. If the new DR does not support this specification, there is no
need for any special handling as the new DR would take over as it
does today. It would assert as soon as it gets elected as DR and
the old DR would become the assert loser as it had already
adjusted its assert metric to PIM_ASSERT_INFINITY - 1
4. PIM Hello option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = TBD | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Graceful DR handoff Hello Option
where
Type : DR Graceful handoff
Length: 2
5. IANA Considerations
A new PIM Hello option is TBD..
6. Security Considerations
Security of the new PIM Hello Options is only guaranteed by the
security of PIM Hello message, so the security considerations for PIM
Hello messages as described in PIM-SM [RFC4601] apply here.
7. Acknowledgement
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8. Contributors
In addition to the authors listed on the front page, the following
co-authors have also contributed to original idea.
Krishna Muddenahally Ananthamurthy
Cisco Systems
Sameer Gulrajani
Cisco systems
Rishabh Parekh
Cisco systems
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601,
DOI 10.17487/RFC4601, August 2006,
<https://www.rfc-editor.org/info/rfc4601>.
[RFC6395] Gulrajani, S. and S. Venaas, "An Interface Identifier (ID)
Hello Option for PIM", RFC 6395, DOI 10.17487/RFC6395,
October 2011, <https://www.rfc-editor.org/info/rfc6395>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
9.2. Informative References
[HELLO-OPT]
IANA, "PIM Hello Options", IANA PIM-HELLO-OPTIONS, March
2007.
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Authors' Addresses
Mankamana Mishra
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: mankamis@cisco.com
Stig Venaas
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: svenaas@cisco.com
Mahesh Sivakumar
juniper networks
1133 Innovation Way
Sunnyvale, CALIFORNIA 94089
UNITED STATES
Email: sivakumar.mahesh@gmail.com
Zheng(Sandy) Zhang
ZTE Corporation
No. 50 Software Ave, Yuhuatai Distinct
Nanjing
China
Email: zhang.zheng@zte.com.cn
Mikael Abrahamsson
Email: swmike@swm.pp.se
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